Abstract: A control system has a central unit for applying DC operating current and control signals to a two line bus. The central unit applies a DC operating current to the bus, as well as signals that have first and second parts. A terminal connected to the bus detects first signal parts on the bus that are unique to that terminal, and, in response thereto, applies the second signal parts to its output terminals. A manual control unit is connected to receive operating current and signals from the output terminals. The manual control unit has a plurality of keys connected to load the bus, and is responsive to determined second signal parts for inhibiting such loading of the bus, thereby enabling the central unit to determine and address of the manual control unit.

Abstract: The disclosure is directed to a photographic printing easel adapted especially for use in connection with the preparation of dye transfer color separations, to the end that the use of the dye transfer process is rendered significantly more convenient and expeditions. The easel includes a test board on one side and an exposure board on the other, with provisions for assuring a common plane of reference on opposite sides. On the test board side, the easel includes a plurality of filter openings through which a series of color test exposures is made in sequence, enabling the final color separation exposures to be properly carried out. Inasmuch as the test exposures for the dye transfer process must be carried out in total darkness, without benefit of any kind of darkroom light, the easel assembly is constructed to accommodate convenient and accurate performance of a series of color separation test exposures in sequence under conditions of total darkness.